// Server1 is a minimal "echo" server.
package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"log"
	"math"
	"math/rand/v2"
	"net/http"
	"strconv"
)

func main() {
	http.HandleFunc("/", handler) // each request calls handler
	log.Fatal(http.ListenAndServe("0.0.0.0:8080", nil))
}

func handler(w http.ResponseWriter, r *http.Request) {
	lissajous(w, r)
}

var palette = []color.Color{color.White, color.Black}

const (
	WhiteIndex = 0
	BlackIndex = 1
)

func lissajous(out io.Writer, r *http.Request) {

	cycles := 5.0
	if cyclesStr := r.URL.Query().Get("cycles"); cyclesStr != "" {
		if val, err := strconv.ParseFloat(cyclesStr, 64); err == nil {
			cycles = val
		}
	}

	const (
		res     = 0.001
		size    = 100
		nframes = 64
		delay   = 8
	)

	freq := rand.ExpFloat64() * 3.0
	anim := gif.GIF{LoopCount: nframes}
	phase := 0.0
	for i := 0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2*size+1, 2*size+1)
		img := image.NewPaletted(rect, palette)
		for t := 0.0; t < cycles*2*math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), BlackIndex)
		}
		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}
	gif.EncodeAll(out, &anim)
}
